Gas stations normally have a number of underground fuel reservoirs which generally are installed about 3 feet below the ground level and include a threaded pipe at the top of the reservoir which permits access thereto for fuel level measurements.
Fuels have a high coefficient of volumetric expansion with temperature. This causes variations in the volume of the fuel contained therein as fuel temperature changes, even if there is no entry or exit of fluid in the reservoir. This variation could be easily mistaken as fuel input or discharge.
On the other hand, fuel leaks should be detected to protect the environment and personnel safety. International regulations (for instance, EPA Standard Evaluation) establish strict limits to minimum detectable leaks. These values could be as low as 0.38 liters per hour of leakage in a 30,000 liter reservoir.
Although fuel pumps can measure the quantity of fluid being dispended from a reservoir, pumps do not take into account the temperature of the fluid, nor the entry of fluid into the reservoir, nor possible leakage or pilfering that could take place. These requirements could be met only by high precision measuring systems enabling computerized processing of level and temperature readings carried out automatically and continuously.